A conventional digital receiving device, which is adapted to remove a correlative noise signal (ambient noise), is disclosed in JP2001-4736A2, especially in FIG. 4 thereof. FIG. 3 is a block view generalizing the digital receiving device disclosed in the aforementioned application publication. As illustrated in FIG. 3, a digital receiving device 70 receives a desired signal S containing a correlated noise signal N by one antenna 71. The noise signal N is considered as an ambient noise. The digital receiving device 70 further down converts a signal transmitted from the antenna 72 to a signal at a predetermined frequency band by a high frequency conversion unit 72, forms a digital signal (S″+N″) by analog/digital converting this signal at the predetermined frequency band by an analog/digital conversion unit (hereinafter, referred to as A/D conversion unit) 73. The digital signal (S″+N″) corresponds to the desired signal S containing the noise signal N. The digital signal (S″+N″) is outputted to a noise removable unit 74. Meanwhile, the digital receiving device 70 still further receives the noise signal N by the other antenna 75, down converts a signal transmitted from the antenna 75 to a signal at a predetermined frequency band by a high frequency conversion unit 77 of a reference noise signal outputting unit 76, and forms a reference noise signal Nr correlated to the noise signal N by analog/digital converting this signal at the predetermined frequency band at an A/D converting unit 78. The reference noise signal Nr is outputted to the noise removable unit 74.
The noise removable unit 74 forms a noise remove signal AN based upon the reference noise signal Nr at an adaptive filter portion 79, and removes the noise signal N by adding the noise remove signal AN and the digital signal (S″+N″) at an adder 80. A filter coefficient of the adaptive filter portion 79 is sequentially updated so as to reduce the noise signal N (N″) at a maximum degree by a filter coefficient updating portion 81.
A need exists for providing a digital receiving device and a radio communication system, both of which can effectively reduce an ambient noise without an enlargement of a circuit thereof.